The present invention relates to a permanent magnetic field starter motor in which permanent magnets are used as a magnetic field and in particular to a permanent magnetic field starter motor having improved position alignment accuracy between permanent magnets and a brush member.
In a permanent magnetic field starter motor according to the prior art, first of all permanent magnets are arranged an inner peripheral face of a yoke. Next, a brush member is arranged on a brush member holder plate and the brush member holder plate is aligned in position and fixed to a rear bracket using screw members. After that, by aligning the rear bracket (to which the brush member holder plate is fixed) and the yoke (to which the permanent magnets are arranged,) the permanent magnets and the brush member are aligned in position.
As the techniques relating to the above stated kinds of the permanent magnetic field starter motor apparatus are disclosed in, for example Japanese patent laid-open publication No. Sho 64-77,446, Japanese patent laid-open publication No. Hei 7-123,628 and Japanese patent laid-open publication No. Hei 6-284,626.
However, in these conventional permanent magnetic field starter motor techniques, arrangement of the permanent magnets and the brush member at a predetermined position (such as between the permanent magnets and the yoke; the yoke and the rear bracket; the rear bracket and the brush member holder plate; and the brush member holder plate and the brush member) requires three components (the yoke, the rear bracket, and the brush member holder plate) in addition to the permanent magnets and the brush member. Further, to arrange the permanent magnets and the brush member at the predetermined position, four positioning alignments are required.
Positioning alignment errors between the respective components affect the positioning accuracy between the permanent magnets and the brush member. As a result, the position of the brush member against the permanent magnets slips off, so that a desirable performance of the permanent magnetic field starter motor can not obtained.
When positioning accuracy between the respective components is increased, the above stated problem would be resolved; however, the manufacturing cost of the permanent magnetic field starter motor becomes high, and as a result the price of the permanent magnetic field starter motor also becomes high.